Struggling to locate __proto__ of the global object known as "window."

Currently I am using Google Chrome browser.

console.log(window.__proto__.__proto__.__proto__);

console.log(window.__proto__.__proto__.__proto__ === EventTarget.prototype);

The first code mentioned above returns EventTarget.prototype for me.

This can be confirmed with the second code, which returns "true."

Furthermore, the following code also evaluates to true:

console.log(EventTarget.prototype.__proto__ === Object.prototype);

However, issues arise when attempting to identify the child of EventTarget.prototype.

console.log(window.__proto__.__proto__);

The code above results in:

WindowProperties {Symbol(Symbol.toStringTag) : "WindowProperties" .....}

When trying to locate the constructor "WindowProperties()" or the object "WindowProperties.prototype",

the console outputs

Uncaught ReferenceError: WindowProperties is not defined at :1:13

Why does this error occur?

javascriptgoogle-chromedomprototypeglobal-object

Answer №1

There is no access to a global called WindowsProperties from your code, even if it exists with a specific name. This situation can be seen in the following example:

const example = (() => {
    return new class Something { };
})();
console.log(example.__proto__.constructor.name); // Something
console.log(Something); // ReferenceError: Something is not defined

It is worth noting that the usage of __proto__ in the code above is for demonstration purposes only. It is recommended to use Object.getPrototypeOf (and, if necessary, Object.setPrototypeOf) instead of __proto__, as it is a deprecated feature present in browsers and not universally supported by all objects.

Intrigued by your code, I explored the lineage of window in Chrome and came up with the following snippet:

const seenBefore = new Set();
let indent = "";
let obj = window;
while (obj) {
    const proto = Object.getPrototypeOf(obj);
    if (seenBefore.has(proto)) { 
        console.log("Encountered a previously seen object; exiting loop");
        break;
    }
    seenBefore.add(proto);
    console.log(`${indent}${proto?.constructor?.name}`);
    indent += "  ";
    obj = proto;
}

Output on Chrome:

Window
  WindowProperties
    EventTarget
      Object
        undefined

Output on Firefox differs slightly:

Window
  EventTarget
    EventTarget
      Object
        undefined

Answer №2

When typing window._ proto _ @ console, the result is displayed on the screen.

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